The present invention relates generally to communications systems, and more specifically to a failure restoration method and a self-healing communications network with distributed automatic rerouting capabilities upon occurrence of a failure.
Known self-healing techniques are divided broadly into two classes. One is a centralized control system that provides overall rerouting control from the central location of a network. In this approach, the rerouting algorithm and the establishing of alarm collection times become increasingly complex as the number of failed channels increases, and a substantial amount of time will be taken to collect alarm signals and to transfer rerouting information should a large number of channels of a multiplexed transmission system fail. The other is a distributed approach in which the rerouting functions are provided by distributed points of the network. The following papers on distributed rerouting approach have been published:
Document 1: W. D. Grover, "The Selfhealing Network", Proceedings of Grobecom '87, November 1987.
Document 2: H. C. Yang and S. Hasegawa, "Fitness: Failure Immunization Technology For Network Service Survivability", Proceedings of Globecom '88, December 1988.
Document 3: H. R. Amirazizi, "Controlling Synchronous Networks With Digital Cross-Connect Systems", Proceedings of Globecom '88, December 1988.
Document 1 is concerned with a restoration technique for failures in a single transmission system, and Document 2 relates to a "multiple-wave" approach in which route-finding packets are broadcast in multiple wave fashion in search of a maximum bandwidth until alternate routes having the necessary bandwidth are established. One shortcoming of this multiple wave approach is that it takes a long recovery time. Document 3 also relates to fault recovery for single transmission systems and has a disadvantage in that route-finding packets tend to form a loop and hence a delay is likely to be encountered.